Sophora flavescens, as a traditional herbal medicine, has been used to treat with a variety of disesases, In previous reports, S. flavescens and sophoraflavanone G (a prenylated flavonoid from S. flavescens) inhibited cytokines productions in LPS-induced Raw 264.7 macrophages cells and BV2 microglial cells. We examined on the anti-allergic effect of S. flavescens on the PMA plus A23187-induced rat leukemia (RBL-2H3) cells. S. flavescens inhibited the release of $eta$-hexosaminidase and productions and expressions of tumor necrosis factor (TNF)-$alpha$, interleukin (IL)-4 and cyclooxygenase (COX)-2 in a dose-dependent manner on stimulated RBL-2H3 cells, however, S. flavescens not affect cell viability. The protein expression level of nuclear factor (NF)-${kappa}B$ (p65) was decreased in the nucleus and suppressed the degradation of inhibitory protein $I{kappa}B-{alpha}$ protein, the activation of extracellular signal-regulated kinases (ERK) mitogen-activated protein kinase (MAPK) by S. flavescens. These results suggest that S. flavescens could be involved anti-allergic effect by control of $NF-{kappa}B$ (p65) translocation into the nucleus through inhibition of $I{kappa}B-{alpha}$ degradation and suppression of pro-inflammatory cytokines expression.